1. Field of the Invention
The present invention relates to a method for applying liquid such as developing solution (developer) and resist solution to substrates, particularly semiconductor wafers.
2. Description of the Related Art
As the conventional liquid applying method, there can be mentioned the apparatus for use with the semiconductor device manufacturing system to coat resist solution to semiconductor wafers.
This liquid applying apparatus usually comprises a processing unit including a spin chuck for sucking, holding and rotating the semiconductor wafer and a cup for housing the semiconductor wafer on the spin chuck therein to conduct the process of developer or resist solution relative to the semiconductor wafer, and a nozzle for dispensing the developer or resist solution onto the semiconductor wafer in the cup.
The resist solution is dropped onto the semiconductor wafer through the nozzle and the semiconductor wafer is rotated at high speed by the spin chuck, so that resist film can be uniformly coated on the semiconductor wafer by centrifugal force thus created.
In the case of this apparatus, one nozzle is used for one processing unit and after the developer or the resist solution is sprayed or dispensed onto the semiconductor wafer through the nozzle, the nozzle is held ready for a next process until a series of coating steps relative to the semiconductor wafer are finished. After these liquid applying steps relative to the semiconductor wafer are finished, a next semiconductor wafer is carried into the processing unit and the nozzle dispenses the developer or the resist solution onto this semiconductor wafer. Therefore, the interval at which the resist solution is dispensed onto the semiconductor wafers through the nozzle becomes long and that part of the developer or the resist solution which is at the tip of the nozzle is likely to become hard while the nozzle is waiting for a next dispensation of the resist solution. This hardening of the resist solution causes the semiconductor wafers not to be uniformly coated with the resist solution and the quality of products not to be kept certain. The yield of products is thus made low.
As disclosed in Published Unexamined Japanese Patent Applications No. 58-124241 and No. 62-195118, there is conventionally well-known another coating apparatus intended to make its processing efficiency two times by using two processing units. Even in the case of this apparatus, however, one resist nozzle is also used only for one processing unit. As already mentioned above, therefore, the interval of dispensing the developer or the resist solution onto the semiconductor wafers is also long and the yield of products is thus made low by the hardening of the resist solution at the tip of the nozzle.
Further, the whole of the apparatus becomes complicated in structure. In addition, the resist liquid coating process cannot be uniformly applied to the semiconductor wafers because the two resist nozzles are independently used for their corresponding processing units.
Still further, solution drops separated from the wafer by centrifugal force are splashed back by inner walls of the cup to again adhere to the wafer. This causes the wafer to be irregularly developed. In addition, solution drops are likely to come outside the cup and the surroundings of the cup are thus contaminated in the conventional cases.